A. Field of the Invention
The present invention is directed to the field of video coding and, more specifically, to scalable video coding.
B. Background
Conventional video coding standards (e.g. MPEG-1, H.261/263/264) involve encoding a video sequence according to a particular bit rate target. Once encoded, the standards do not provide a mechanism for transmitting or decoding the video sequence at a different bit rate setting to the one used for encoding. Consequently, when a lower bit rate version is required, computational effort must be devoted to (at least partially) decoding and re-encoding the video sequence.
In contrast, with scalable video coding, the video sequence is encoded in a manner such that an encoded sequence characterized by a lower bit rate can be produced simply through manipulation of the bit stream; in particular through selective removal of bits from the bit stream.
In U.S. patent application Ser. No. 10/797,467, one system was proposed to efficiently convert a video sequence to a binary representation that describes a video sequence progressively in quality, while the correlation within a frame or among frames is efficiently exploited. Other conversion schemes to produce binarization results of video sequences are also available.
The present invention focuses on the strategies used in decoding such binarization results from a bit stream, and in decoding such results from a bit stream. Particularly it focuses on coding the binarization results into a bit stream, and decoding such results from a bit stream, using context-based adaptive binary arithmetic coding. An even more specific scalable video decoder is developed based on H.264 with a Context-based Adaptive Binary Arithmetic Coding (CABAC) engine (ITU-T Recommendation, H.264, “Advanced video coding for generic audiovisual services”, pre-published, May 30, 2003, also known as Advanced Video Coding (AVC), or MPEG-4 part-10).